On my personal bikes I have yet to have a UN55 BB fail or get to the point of needing a repack. One of the BB's I have has been faithfully serving for at least 20 years and has been on 4 bikes, including one mountain bike where it started its service life.
Only replaced a half dozen of them on customer's bikes in that same time. I like the idea of rebuilding stuff, and now that I see the thing only has 7 balls per side, I am baffled how that BB has been so durable.